Vehicle anti-brake blocking or anti-skid systems frequently use an evaluation circuit which determines of brake fluid, supplied from a pressure source, is to be admitted to the brake cylinders of vehicle brakes, to be drained from the brake cylinders, or if already pressurized brake fluid is to be maintained under existing pressure conditions. Control systems of this kind may additionally use braking pressure control valves to vary the braking pressure. A static brake fluid circuit may be present and, due to circulation of brake fluid in brake fluid circuits, excessive drainage of brake fluid in the static circuit may occur.